An increased prevalence in the use of high intensity discharge (HID) lights as headlights has been accompanied by an increased number of driver complaints to the National Highway Traffic Safety Administration (NHTSA) about headlight glare. DOT HS 809 669 Drivers' Perceptions of Headlight Glare from Oncoming and Following Vehicles (January 2004). Both the higher intensity of light and the greater proportion of light in the blue spectrum from HID headlights contribute to a greater degree of discomfort glare relative to that produced by standard halogen headlights.
The use of Light-Emitting Diodes (LED) headlights is also becoming more prevalent. And as with HID headlights, LED headlights produce a greater proportion of light in the blue spectrum than standard halogen headlights, which causes greater discomfort glare. Additionally researchers have determined that human exposure to LED light, without the protection of a blue light absorbing filter, increases the risk of retinal degenerative diseases, mainly Age Related Macular Degeneration (AMD). Thus some researchers recommend eye protection to limit exposure to blue light. Chamorro E, Carralero S F, Bonnin-Arias C, Pérez-Carrasco M J, de Luna J M, et al. (2013) Photoprotective Effects of Blue Light Absorbing Filter against LED Light Exposure on Human Retinal Pigment Epithelial Cells In Vitro, J Carcinog Mutagen S6: 008.
U.S. Pat. No. 2,397,947 by W. H. Cobert, discloses the prismatic mirror, which continues to be the primary apparatus for reducing glare reflected by a rear view mirrors into a drivers' eyes. The prismatic mirror comprises a wedged shaped glass front surface with a silver reflective backing. As the glass front surface and the silver reflective backing are not parallel, light is reflect off the front and back surfaces at different angles. The back surface reflects brightly as a silvered mirror. The front surface reflects weakly, in the same way that an un-silvered glass window against a dark background produces a weak reflection. In nighttime mode the mirror is tilted such that the light weakly reflected off the front of the glass is angled towards eye level. Conversely, in daytime mode the mirror is tilted so the light brightly reflected off the silver backing is angled towards eye level. The simplicity and low cost of this glare deflecting apparatus has contributed to its longstanding use. However, it does entail the disadvantage of requiring the driver's attention to switched it between day and night modes and it does not filter blue light.
Electrochromic automatic dimming mirrors eliminate the manual switching between modes typically required with prismatic rearview mirrors. However Electrochromic mirrors consume electric power; require wiring; and are more expensive and more vulnerable to malfunction. For example, when the electrochromic material is a liquid there is a potential for leaks.
Yellow tinted night driving glasses, such as those disclosed in Chinese patent CN 202815350, present an inexpensive apparatus for shielding a driver from glare and blue light. However, they also impose the danger that the driver's vision will be impaired in certain respects. For example, the glasses may prevent him from seeing yellow LED warning lights and traffic signals.
Therefore, there exists a need for a nonelectric, reliable, inexpensive, and safe device to shield vehicle drivers and occupants from the glare and blue light emanating from HID and LED headlights of other vehicles.